This invention relates to a box pad for mounting electrical equipment to provide a foundation to support the weight of a transformer or to produce a vault area for electrical or other connections.
Box pads serve as structural enclosures to support transformers and house electrical wiring for the utility industry. The principal function of the box pad is to provide a foundation to support the weight of a transformer and to produce a vault area for electrical cable connections. The box must be rigid enough to minimize deflection under the load of a transformer, durable enough to maintain its integrity through seasonally harsh environments, and safe to surrounding inhabitants. A box pad must also provide a rigid top surface for mounting and fastening electrical components. The performance criteria for box pads can be found in Northeast Underground Guideline Number 9001-87R1 xe2x80x9cBox Pad Style Formations for Single Phase Transformersxe2x80x9d (NEUG), and in Western Underground Guidelines (WUG), particularly the xe2x80x9cWestern Underground Committee Guidexe2x80x9d sections 2.15 and 3.6, which are incorporated herein by reference.
Common ways of producing transformer box pads in composites include compression molding of glass preform or sheet molding compound, spray-up (with or without robotics) of glass chopped fibers, die molding of polymer resin concrete, injection molding of structural foam, and concrete.
Spray-up methods have more flexibility in production, however this process results in much more variability in fiber distribution throughout the structure. Box pads formed by spray-up methods can vary in thickness and quality. Structural foam parts have good dimensional stability but they are difficult to mold less than six millimeters thick, so volume must be compromised. Also, without reinforcing fibers, foam parts tend to creep over time. Concrete and polymer concrete products provide rigidity but are at least three times heavier than composite products.
Typical spray-up and some polymer resin concrete designs have a gel coating applied on the external surface to provide UV protection. However, if the coating is scratched or wears away the exposed material can quickly decay in normal environmental conditions. Experiments with polymer resin concrete have shown that without protection, the box pad material losses 25% of its stiffness in a period of about a year in normal sunlight. It has also been shown that this box pad material can lose over 35% of its strength in a half a year in wet and salty conditions, and suffers similar losses with certain acid exposures.
Compression molding of fiberglass with a polyester binder nets the highest glass content for the highest stiffness, and uses a closed mold yielding the most consistent wall thickness. This accuracy produces parts with much less variation in strength, stiffness, and weight. Compression molding has the additional benefits of rapid production times and permanent UV protection that is chemically introduced into the resin. Since higher production rates generate faster delivery times at a lower cost, and greater strength yields durability and longer life with less failure, compression molding is a good practice for quality parts at a reasonable price.
It is therefore an object of this invention to provide such a box pad for mounting electrical equipment which is lightweight, strong, and which has superior bending stiffness.
It is a further object of this invention to provide such a box pad for mounting electrical equipment which is safe and durable and has uniform thickness, consistent quality, and long life.
It is a further object of this invention to provide such a box pad for mounting electrical equipment which has excellent aging properties and very good resistance to water, acid, oils, fuels and ultraviolet radiation.
It is a further object of this invention to provide such a box pad for mounting electrical equipment which can be produced and manufactured more rapidly and economically.
It is a further object of this invention to provide such a box pad for mounting electrical equipment which allows for simpler, quicker and safer installation.
It is a further object of this invention to provide such a box pad for mounting electrical equipment which provides for cost savings in the manufacturing, shipping, and installation stages.
It is a further object of this invention to provide such a box pad for mounting electrical equipment which is robust, durable and environmentally inert.
It is a further object of this invention to provide a box pad for mounting electrical equipment which meets or exceeds the NEUG and WUG guidelines.
The invention results from the realization that a stronger, lighter weight, long-lasting box pad for mounting electrical equipment which meets the NEUG and WUG guidelines, and which is more easily manufactured, shipped and installed, can be achieved with inclined, corrugated walls comprised of a lightweight material such as a thermoplastic, glass fiber composite, or other lightweight advanced composite material.
This invention features a box pad for mounting electrical equipment including a base section, a support, a support section adapted for mounting electrical equipment, and an inclined corrugated wall section extending between said base and support sections.
In a preferred embodiment, the wall section is inclined at greater than zero degrees but less than eleven degrees. The wall section may be inclined at about five degrees. The wall section or the base and support sections may be made of a glass fiber composite. The ratio of the depth of corrugation to the thickness of the wall section may be less than four to one. The corrugations may extend along the wall section from the base section toward the support section, and may extend all the way along the wall section between the base section and the support section. The corrugations may be evenly spaced about the wall section. The wall section may include four wall elements arranged in a trapezoidal configuration. The wall section may be made of a material with a specific gravity of less than 1.3, or a material with a specific gravity of less than 1.3 and with a ratio of tensile modulus to specific gravity of approximately four to one. The wall material maybe made of a binder filled with fiberglass, or a thermoplastic, glass fiber composite.